Håvard Arnestad

• Arnestad, Håvard; Gereb, Gabor; Lønmo, Tor Inge Birkenes; Kirkebø, Jan Egil; Austeng, Andreas & Näsholm, Sven Peter (2022). Sonar array beampattern bounds and an interval arithmetic toolbox. Proceedings of Meetings on Acoustics (POMA). ISSN 1939-800X. doi: 10.1121/2.0001613. Vis sammendrag

  The framework of interval arithmetic (IA) and its extension to complex numbers has in the last decade been applied as a tool for finding robust tolerance bounds of antenna arrays. The IA framework complements statistical methods, as inclusive upper and lower bounds of the beampattern are obtained directly, only assuming error bounds on specifically chosen array parameters. Recently, beampattern synthesis for sonar arrays subject to amplitude excitation errors has been extended from linear arrays with omnidirectional elements to non-linear arrays with directive elements. In this work, we demonstrate that the analysis can be developed further to include both amplitude and phase errors. Moreover, we account for error bounds in element position and orientation, thus representing a more comprehensive method for evaluating the worst-case performance due to uncertainty bounds in a multitude of design parameters. For this purpose, we have created an open-source MATLAB toolbox to calculate beampattern bounds for an array with bounded error tolerances. The toolbox features an object oriented library of interval classes and an interactive graphical user interface with easily configurable settings, where results for different interval representations are shown along with their corresponding bounds. The beampattern bounds of a sonar array is illustrated through an example.

• Viggen, Erlend Magnus & Arnestad, Håvard (2022). Inhomogeneous P- and S-wavefields radiated into isotropic elastic solids. I Viggen, Erlend Magnus (Red.), Proceedings of the 45th Scandinavian Symposium on Physical Acoustics. Norsk Fysisk Selskap. ISSN 978-82-8123-022-4. Fulltekst i vitenarkiv
• Arnestad, Håvard Kjellmo & Viggen, Erlend Magnus (2021). A fast semi-analytical method for propagating leaky Lamb wavefields. I Viggen, Erlend Magnus (Red.), Proceedings of the 44th Scandinavian Symposium on Physical Acoustics. Norsk Fysisk Selskap. ISSN 978-82-8123-021-7. Fulltekst i vitenarkiv
• Viggen, Erlend Magnus & Arnestad, Håvard Kjellmo (2021). Understanding sound radiation from surface vibrations moving at subsonic speeds. I Viggen, Erlend Magnus (Red.), Proceedings of the 44th Scandinavian Symposium on Physical Acoustics. Norsk Fysisk Selskap. ISSN 978-82-8123-021-7. Fulltekst i vitenarkiv

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• Arnestad, Håvard; Gereb, Gabor; Birkenes Lønmo, Tor Inge; Kirkebø, Jan Egil; Austeng, Andreas & Näsholm, Sven Peter (2022). Sonar array beampattern bounds: tolerance analysis using interval arithmetic.
• Arnestad, Håvard & Viggen, Erlend Magnus (2022). A fast method for simulating Lamb wave propagation in coupled non-parallel plates.
• Viggen, Erlend Magnus & Arnestad, Håvard (2022). Intensity of inhomogeneous waves in simple solids.
• Arnestad, Håvard Kjellmo & Viggen, Erlend Magnus (2021). A fast semi-analytical method for propagating leaky Lamb wavefields. Vis sammendrag

  A fast method is presented for calculating the wavefields from initialized leaky Lamb waves on plates immersed in sufficiently light fluids. The method works by precomputing the dispersion relation and attenuation, and propagating the wavefields in the frequency domain. An angular spectrum approach is used to include leakage into surrounding fluid. Compared to matching FEM simulations, the computations are performed in the order of seconds, rather than hours. The method also benefits from being much easier to set up correctly, but is on the other hand less general in that it cannot handle e.g. scattering from defects. The correspondence is shown to be good for the case of interest.

• Viggen, Erlend Magnus & Arnestad, Håvard Kjellmo (2021). Understanding sound radiation from surface vibrations moving at subsonic speeds.

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